Terminal monitors used with mainframe and personal computers and in various types of data services display various configurations of information generated by the computers and data services. Typically, such monitors are cathode-ray tubes, conventionally known as CRTs, wherein a slender beam of electrons are generated and projected on a fluorescent screen to produce a luminous spot representing information. In one configuration, a CRT display can be thought of as a page consisting of 24 rows of characters wherein each row is 80 characters in lenght. Each character is formed from an array of "dots" or "pixels" which may be configured to form numbers, letters and special symbols.
Pixels are formed on the CRT screen by turning an electron beam on and off such that a visible pixel appears on the screen when the electron beam is turned on. The electron beam is controlled by a video display device which responds to input data representing a display by controlling the CRT to move the beam horizontally and vertically across the screen and to turn the electron beam on and off thereby enabling the CRT screen to portray pixels making up the display.
In the manufacture of video controller devices, each device is tested by applying digital data defining a specific test pattern to the video controller device. The video controller device responds to the applied data by enabling a terminal CRT screen to portray the output generated by the tested video controller device. Human observation is used to compare the display generated by the tested video controller device with the specific test pattern. A problem arises in that advanced designs of video controller devices portray displays in high resolution CRTs that make human observation difficult to determine errors that may occur between a pattern generated by a defective video controller device and the specific test pattern.
Character recognition apparatus has been devised for use in identifying characters represented by pixel arrays. Such apparatus identifies a character by forming a window around the pixel array and roughly identifies a character encoded within the array by counting pixels inwardly from the top and bottom and from each side of the array until a transition is reached from off to on. The pixel count information is combined and weighted in order to determine that the array may be one of a particular set of characters. A problem arises in that this use of pixel counting apparatus only represents the outer edges of a display and must be combined and weighted to identify a character. Such apparatus does not identify details of the center of a test pattern thereby failing to detect errors that may be present in a tested video display device. Such apparatus is not concerned with video controller devices used to portray displays on color CRTs and would not distinguish between color pixels used for multi-color displays.